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732 Chapter 42 ______________________ 1945 Guide Stacks Stacks or vertical flues are really chimneys and utilize both the in ductive effect of the wind and the force of temperature difference. Like the roof ventilator, the stack outlet should be located so that the wind may act upon it from any direction. With little or no wind, chimney effect depends on temperature difference to produce a removal of air from the rooms where the inlet openings are located. GENERAL RULES A few of the important requirements in addition to those already outlined are: 1. Inlet openings in the building should be well distributed, and should be located on the windward side near the bottom, while outlet openings are located on th^leeward side near the top. Outside air will then be supplied to the zone to be ventilated. 2. Inlet openings should not be obstructed by buildings, trees, sign boards, etc., outside nor by partitions inside. 3-'_ Greatest flow per square foot of total opening is obtained by.Rising inlet and outlet openings of nearly equal areas. 4. In the design of window ventilated buildings, where the direction of the wind is quite constant and dependable, the orientation of the building together with amount and grouping of ventilation openings can be readily arranged to. take full advantage of the force of the wind. Where the wind's direction is quite variable, the openings should be arranged in sidewalls and monitors so that, as far as possible, there will be approxi mately equal areas on all sides. Thus, no matter what the wind's direction, there will always be some openings directly exposed to the pressure force and others to a suction force, and effective movement through the building will be assured. 5. Direct short circuits between openings on two sides at a high level may clear the air at that level without producing any appreciable ventilation at the level of occupancy. 6. In order that temperature difference may produce a motive force, there must be vertical distance between openings. That is, if there are a number of openings available in a building, but all are at the same level, there will be no motive {lead produced by temperature difference, no matter how great that difference might be. . 7. In order that the force of temperature difference may operate to maximum ad vantage, the vertical distance between inlet and outlet openings should be as great as possible. Openings in the vicinity of the neutral zone are less effective for ventilation. 8. In the use of monitors, windows on the windward side should usually, be kept closed, since, if they are. open, the inflow tendency of the wind counteracts the outflow tendency of temperature difference. Openings on the leeward side of the monitor result in cooperation of wind and temperature difference. 9. In an industrial building where furnaces that give off heat and fumes are to be installed, it is better to locate them in the end of the building exposed to the prevailing. wind. The strong suction effect of the wind at the roof near the windward end will then cooperate with temperature difference, to provide for the most active and satisfactory removal of the heat and gas laden air. 10. In case it is impossible to locate furnaces in the windward end, that part of the building in which they are to be located should be built higher than the rest, so that the wind, in splashing therefrom will create a suction. The additional height also increases the effect of temperature difference to cooperate with the wind. 11. The intensity of suction or the vacuum produced by the jump of the wind is greatest just back of the building face. The area of suction does not vary with the wind velocity, but the flow due to suction is directly proportional to wind velocity. 12. Openings much larger than the calculated areas are sometimes desirable, especially when changes in occupancy are possible, or to provide for extremely hot days. In the former case, free openings should be located at the level of occupancy for psychological reasons. 13. In single story industrial buildings, particularly those covering large areas, natural ventilation must be accomplished by taking air in and out of the roof openings. Openings in the pressure zones can be used for inflow and openings in the suction zone, or openings in zones of less pressure, can be used for outflow. The ventilation is accomplished by the manipulation of openings to get.air flow through the zones to be ventilated. A'qtural Ventilation -- ------- -733-- --------------------u DAIRY BARN VENTILATION3 A successful barn ventilating system is one which continuously supplies the proper amount of air required by the stock, with proper distribution and without drafts, and one which removes the excessive heat, moisture, and odors, and maintains the air at a proper temperature, relative humidity, and degree of cleanliness. Barn temperatures below freezing and above 80 F affect milk produc tion. Milk producing stock should be kept in a bam temperature be tween 45 and 50 F. Dry stock, at reduced feeding, may be kept in a bam 5 to 10 deg higher. Calf barns are generally kept at 60 F, while hospital and maternity barns usually have a temperature of 60 F or somewhat higher. The- heat produced by a cow of an average weight of 1000 lb may be taken as 3000 Btu per hour. The average rate of moisture production by a cow giving 20 lb of milk per day is 15 lb of water per day, or 4375 grains per hour. To set a standard of permissible relative humidity for cow barns is difficult. For 45 F an average relative humidity of 80 per cent is satisfactory, with 85 per cent as a limit. Where the bam volume is within the limit that can be heated by the stabled animals, the air supply need not be heated. The air should be supplied through or near the ceiling. It is better to have the exhaust openings near the floor as larger volumes of warm air are then held in the barn and there is better temperature control with less likelihood of sudden change in barn temperature. If a cow weighs 1000 lb and produces 3000 Btu of heat per hour, and if a barn for the cow has 600 cu ft of air space with 130 sq ft of building. exposure, one cow will require 2600 to 3550 cu ft per hour of ventilation, depending on the temperature zone in which the barn is located. The permissible heat losses through the structure, based on one cow. and de pending on the temperature zone, vary between 0.043 and 0.066 Btu per hour per cubic foot of barn space, and 0.197 to 0.305 Btu per hour per square foot of barn exposure. GARAGE VENTILATION On account of the hazards resulting from carbon monoxide and other physiologically harmful or combustible gases or vapors in garages,, the importance of proper ventilation of these buildings cannot be over emphasized. During the warm months of the year, garages are usually ventilated adequately because the doors and windows are kept open. As cold weather sets in, more and more of the ventilation openings are closed and consequently on extremely cold days the carbon monoxide concentra tion runs high. Many garages can be satisfactorily ventilated by natural means par ticularly during the mild weather when doors and windows can be kept open. However, the A.S.H.V.E. Code of Minimum Requirements for Heating and Ventilating Garages, adopted in 1935, states that natural ventilation may be employed for the ventilation of storage sections where it is practical to maintain open windows or other openings at all times. The code specifies that such openings shall be distributed as uniformly *Dairy Barn Ventilation, by F. L. Fairbanks (A.S.H.V.E. Transactions, Vol. 34, 1928, p. 181). Cow Barn Ventilation, by Alfred J. Ofiner (A.S.H.V.E. Transactions, Vol. 39, 1933, p. 149). For additional. information on this subject refer to Technical Bulletin. U. $. Department of Agriculture (1930). by M. A. R. Kelley. Also see Air Conditioning of Farm Buildings, by F. L. Fairbanks (Agricultural Engineering, November. 1937. p. 485).